1. Field of the Invention
The present invention relates to a driving circuit of a display device, and more particularly, to a driving circuit of an active matrix electroluminescence device (AMELD) driven by digital signals.
2. Discussion of the Related Art
An AMELD emits light by electroluminescence. The AMELD is manufactured by forming electrodes of matrix type at both surfaces of a flat shaped luminescent layer. The AMELD includes a picture display unit and a driving circuit unit.
The AMELD has characteristics such as wide viewing angle, rapid response time, high contrast, low voltage driving, low power consumption, thinness and lightness in weight. Furthermore, the AMELD can display various colors, so that the AMELD has been attractive as a new generation display device for use in a large sized flat display device.
Display devices have several intermediate states, which range from black and white states to display various colors. At this time, methods for displaying colors are classified in two categories: (1) to adjust voltage intensity applied to a liquid crystal and (2) to adjust current intensity applied to the liquid crystal.
The method for adjusting the voltage intensity applied to the liquid crystal is based on a characteristic in which transmittivity of light varies according to the voltage intensity. That is, picture luminance is changed according to a data voltage with respect to a threshold voltage by adjusting the intensity of an externally applied voltage.
At this time, the threshold voltage is the voltage at which a change of the transmittivity begins occur after a voltage is first applied, i.e. the threshold voltage is the gate voltage needed to establish a conducting channel between the source and drain of an enhancement MOS or PN Diode. If the threshold voltage is high, the voltage intensity applied to the liquid crystal must be increased, thereby increasing power consumption.
The transmittivity is proportional to the voltage intensity according to a curve function. In this case, it is hard to adjust the voltage intensity according to the transmittivity.
To obtain picture images in a display panel, several blocks are set to display gray so that transmittivity is changed according to the voltage intensity applied. At this time, if the blocks are set according to the voltage intensity, intervals of the transmittivity are not constant because the transmittivity is proportional to the voltage intensity in the curved function. Therefore, it is difficult to display gray and to obtain uniformity of the picture images.
Meanwhile, the transmittivity is proportional to the current intensity in a straight line. Therefore, to adjust the current intensity is easier and more accurate than to adjust the voltage intensity.
A driving circuit of a general AMELD will be described with reference to the accompanying drawings.
FIG. 1 is a schematic view showing a structure of the driving circuit of the general AMELD.
As shown in FIG. 1, the driving circuit of the general AMELD includes a power supply 10, an interface unit 11, a memory unit 12, a source driver 15, a gate driver 16 and a timing controller 47.
The power supply 10 supplies power to a display panel. The interface unit 11 transfers an image signal from an external micro controller. The memory unit 12 stores the image signal from the interface unit 11. The source driver 15 outputs the power supplied from the power supply 10 to a data signal of a display panel. Also, the gate driver 16 outputs a scan signal turning on a TFT to apply the data signal to each pixel of the display panel 18. The timing controller 17 generates and controls timing signals required to the source and gate drivers.
The signal source is a computer or a laser disk player for displaying moving pictures.